A network-based or infrastructure based wireless location system location performance is normally expressed as one or more circular error probabilities. Network-based systems rely on the reception of the wireless device originated uplink mobile transmission which is used in a time (time-of-arrival (TOA), time-difference-of-arrival (TDOA)), power (power-of-arrival (POA), power-difference-of-arrival (PDOA)) or angle-of-arrival (AoA) location calculation. Network-based location calculations can be combined with mobile-based measurements, collateral information, or with other network-based location calculations to form hybrid locations.
Early work relating to network-based Wireless Location Systems is described in U.S. Pat. No. 4,728,959; “Direction Finding Localization System” (issued Mar. 1, 1998) which discloses a system for locating cellular telephones using angle of arrival (AOA) techniques and U.S. Pat. No. 5,327,144, (Issued Jul. 5, 1994) “Cellular Telephone Location System,” which discloses a system for locating cellular telephones using time difference of arrival (TDOA) techniques. Further enhancements of the system disclosed in the '144 patent are disclosed in U.S. Pat. No. 5,608,410, (Issued Mar. 4, 1997), “System for Locating a Source of Bursty Transmissions”. Location estimation techniques for wide-band wireless communications systems were further developed in U.S. Pat. No. 6,047,192 (Issued Apr. 4, 200), “Robust, Efficient Localization System”.
All of these patents are assigned to TruePosition, Inc., the assignee of the present invention. TruePosition has continued to develop significant enhancements to the original inventive concepts. First commercially deployed in 1998 by TruePosition in Houston Tex., overlay network-based wireless location systems have been widely deployed in support of location-based services including emergency services location. As realized and noted in extensive prior art, the ability to routinely, reliably, and rapidly locate cellular wireless communications devices has the potential to provide significant public benefit in public safety and convenience and in commercial productivity.
Modification of the radio signaling in a wireless communications system to enhance the performance of a network-based wireless location system (WLS) has previously been contemplated in TruePosition U.S. patents: U.S. Pat. No. 7,689,240; “Transmit-power control for wireless mobile services”, U.S. Pat. No. 6,519,465; “Modified transmission method for improving accuracy for E-911 calls”, U.S. Pat. No. 6,463,290; “Mobile-assisted network based techniques for improving accuracy of wireless location system”, U.S. Pat. No. 6,334,059; “Modified transmission method for improving accuracy for e-911 calls” and U.S. Pat. No. 6,115,599; “Directed retry method for use in a wireless location system”.
The use of collateral information to enhance and enable location determination in further applications of network-based systems was introduced in Maloney, et al., U.S. Pat. No. 5,959,580; and further extended in Maloney, et al., U.S. Pat. Nos. 6,108,555 and 6,119,013. These and related following descriptions of the prior art for network-based location determination systems enable robust and effective location-determination performance when adequate measurement data can be derived or are otherwise available.
The Long-Term Evolution (LTE and LTE-advanced) successors to the Universal Mobile Telephone System (UMTS) are based on the Orthogonal frequency-division multiplexing (OFDM) scheme.
The LTE specification (primarily the 3rd Generation Partnership Program (3GPP) Technical Specification no. 36.305, “Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Stage 2 functional specification of User Equipment (UE) positioning in E-UTRAN) describes several location techniques for LTE wireless devices (User Equipment or UE). As the standardized location functionality provides a means to determine the geographic position and/or velocity of the User Equipment (UE) based on measuring radio signals. The LTE standardized techniques include:                network-assisted GNSS (Global Navigation Satellites Systems)        downlink positioning        enhanced cell ID method.        
Hybrid positioning using multiple methods from the standardized positioning methods is also supported in the LTE technical standards.